JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Conjugate, Modulus and Argument of complex number

  • question_answer
    Let \[{{z}_{1}}\] be a complex number with \[|{{z}_{1}}|=1\] and \[{{z}_{2}}\]be any complex number, then \[\left| \frac{{{z}_{1}}-{{z}_{2}}}{1-{{z}_{1}}{{{\bar{z}}}_{2}}} \right|=\]    [Orissa JEE 2004]

    A) 0

    B) 1

    C) - 1

    D) 2

    Correct Answer: B

    Solution :

    We have \[|{{z}_{1}}|\ =1\] and \[{{z}_{2}}\]be any complex number. \[\Rightarrow \left| \ \frac{{{z}_{1}}-{{z}_{2}}}{1-{{z}_{1}}{{{\bar{z}}}_{2}}} \right|\ =\frac{|{{z}_{1}}-{{z}_{2}}|}{\left| \ 1-\frac{{{{\bar{z}}}_{2}}}{{{{\bar{z}}}_{1}}}\  \right|}\];         \[\because \ {{z}_{1}}{{\bar{z}}_{1}}=\ |{{z}_{1}}{{|}^{2}}\] \[=\frac{|{{z}_{1}}-{{z}_{2}}|}{|{{{\bar{z}}}_{1}}-{{{\bar{z}}}_{2}}|}|{{\bar{z}}_{1}}|\]; Given that  \[\because \ |{{\bar{z}}_{1}}|\ =1\] \[=\frac{|{{z}_{1}}-{{z}_{2}}|}{|\overline{{{z}_{1}}-{{z}_{2}}}|}=\frac{|{{z}_{1}}-{{z}_{2}}|}{|{{z}_{1}}-{{z}_{2}}|}=1\].


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